A participatory GIS approach to flood risk assessment of informal settlements the case of Cape Town

Includes abstract.Includes bibliographical references.Rural-urban migrations have contributed to the steady increase in the population of Cape Town. Many of the migrants have settled in informal settlements because they cannot afford to rent or buy decent housing. Many of these settlements are however located on marginal and often poorly drained land. Consequently, most of these settlements are prone to flooding after prolonged rainfall. Current flood risk management techniques implemented by the authorities of the Cape Town City Council (CTCC) are ideal for formally planned settlements but are not designed to support informal settlements...This study sought to investigate a methodology that the CTCC could use to improve flood risk assessment

도시홍수 저감을 위한 근거기반 계획 : 서울시를 중심으로

학위논문 (석사) -- 서울대학교 대학원 : 농업생명과학대학 생태조경·지역시스템공학부(생태조경학), 2021. 2. 강준석.최근 기후변화로 인해 발생되고 있는 사회/경제적 피해는 급속히 증가하고 있다. 기후변화로 인한 2차적 피해로는 폭염, 홍수 등이 있다. 그중에서 극한 강우는 도심지역에 큰 피해를 발생시키고 있다. 대표적으로는 2011년 발생한 집중호우 등이 있는데, 당시에는 최대 110.5 mm/hr의 기록적인 강수가 내렸다. 현대 도시에서 발생하는 홍수의 대부분 원인은 불투수성 포장면의 급격한 증가와 내수배제 불능, 물순환 시설 부재 등의 원인이 있다. 기상청에서 제공하는 기후변화 시나리오에 따르면, 향후 100년간 도시의 평균 강수량은 줄어들 것으로 파악된다. 하지만, 일시에 폭우가 내리는 빈도가 증가하고 국지성 피해가 뚜렷하게 발생할 것으로 판단된다. 현재 상태의 기반시설들에 보수나 방어기술이 수립되지 않으면, 그 피해는 상당할 것으로 판단된다. 이에 본 연구는 총 세 가지 연구 목표를 수립하여 수행하였다. 첫 번째, 기상청에서 제공하는 기후변화 시나리오(RCP 4.5/RCP 8.5)로 인해 발생할 수 있는 향후 80년(2020년-2100년)의 도시 홍수 피해량을 정량적으로 분석한다. 두 번째, 정량적으로 분석된 피해량에 기반한 재해 저감 시설을 선정하고, 재해의 저감량을 분석한다. 이를 통해 근거 기반(Evidence-Based Planning)의 시설배치 및 설계한다. 재해 저감 시설은 미래 세대가 지속적으로 사용할 수 있는 친환경(Eco-Friendly) 시설물을 선정하였다. 세 번째, HCFD (Hazard Capacity Factor Design) 모델의 개발을 통해, 향후 변화할 수 있는 시설물들의 용량과 성능에 대해 정량적으로 분석한다. HCFD 모델은 저감 기술을 유지하는 방법을 고려하는데 사용된다. 이러한 목표를 달성하기 위해서 방어 기술로 총 세 가지를 도입하였다. 저류조, 투수성 포장 그리고 생태수로가 이에 해당한다. 저류조의 경우, 환경부에서 지정하고 있는 법령을 참고하여 도입 가능한 용량을 파악하였다. 투수성포장과 생태수로는 법령으로 명확히 규정하는 설계 지침이 없기에, 타 연구 보고서를 참고하였다. 각 기술들의 도입 규모를 산정하기 위해서 Arc-GIS ArcHydro Plug in을 사용하였고 Watershed를 분석하였다. Watershed에 영향을 미치는 범위를 파악하기 위해서 기후변화시나리오에서 제공하는 강수량을 시간 단위로 분석하였고, 이를 위해 Huff Curve 공식을 사용하였다. 위에서 언급된 세 가지 기술은 빗물의 저장 용량을 증가시켜 홍수 완화에 기여할 것으로 판단된다. 세 가지 기술을 모두 도입하였을 때 2050년과 2060년에는 RCP 8.5 시나리오의 모든 홍수피해를 저감할 수 있을 것으로 판단된다. 2070년 이후에는 유출이 발생할 것으로 분석되지만, 적응 기술을 통해 홍수를 크게 줄일 수 있을 것으로 예측된다. 본 연구 논문에서는 10년 단위의 홍수와 적응량을 산정하였지만, 추후 후속 연구에서는 1년 단위의 분석이 실시되어야 할 것으로 판단된다. 또한 저류조 내부에 퇴적되는 비점오염원의 청소 시기가 산정되었습니다. 저류조의 경우 MOUSE 회귀 분석을 통해 내부에 축적된 비점오염원 제거 시기를 산정하였다. 빗물 저류조 내부 관리는 크게 주의단계, 일반단계, 안전단계로 지방자치단체를 구분하였다. 주의단계에 해당하는 지방자치단체는 9개, 일반단계에 해당하는 지방자치단체는 10개, 안전단계에 해당하는 지방자치단계는 5개가 해당한다. 이 연구의 결과를 통해 도출된 결론 및 의의는 세 가지로 요약된다. 첫째, 본 연구는 기후변화 시나리오에 따라 발생할 수있는 홍수 가능성을 10년 주기로 분석했다.RCP 8.5 시나리오와 RCP 4.5 시나리오 모두 2070년 이후에 빈번한 홍수의 추이를 볼 수 있었다. RCP 8.5 시나리오의 2090년에 강수량이 가장 많을 것으로 예상된다. RCP 4.5 시나리오 2100년의 경우, 최대 690 mm, 시간당 강수량은 238 mm까지 내릴 것으로 판단된다. 두 번째, 본 연구 논문은 각 기술의 용량을 자치구별로 분석하였다. 본 연구에서 가정한 설치 규정에 따르면 서울시 전역에 설치할 수 있는 빗물 저류조의 부피는 776,588 m³, 투수성 포장은 89,049 m³, 생태수로는 81,986 m³이다. 각 지방자치단체가 두 가지 기술만을 적용하였을 때 효율적인 조합을 제안한 것은 본 연구가 가지는 중요한 의의입니다. 셋째, 각 재해저감 기술로 저감할 수 있는 유출량을 정량화했습니다. 이 연구는 지역 차원의 분산적 형태의 홍수가 더 자주 발생하고, 재난 저감 기술의 정량적 효과를 분석하였다는데 의의가 있다. 본 연구의 한계는 네 부분으로 나눌 수 있다. 첫 번째 한계는 기후변화 시나리오에 대한 불확실성이다. 탄소 배출량이나 시나리오의 변화는 강수량 값을 크게 변경할 수 있기 때문에 오류가 적은 시나리오를 사용하면 향후 연구가 더 중요한 연구로 발전할 것으로 판단된다. 최근 기후변화 시나리오의 불확실성을 줄일 수 있는 연구가 활발히 진행 중이기 때문에, 첫 번째 한계점을 보완한 후속연구가 진행될 것이라 판단된다. 두 번째 한계는 RCP 4.5 / RCP 8.5 시나리오가 10년의 빈도로 수행되었다는 것이다. 세 번째 한계점은 사회 변화 요인이 반영되지 않았다는 것 입니다. 네 번째는 검증의 한계입니다. 본 연구에서는 서울시의 유출수를 계산하기 위해 산술 방정식과 GIS Arc-hydro를 사용하였다.추후 SWMM 등의 홍수 해석 프로그램을 활용하여 추가적인 검증이 되어야 한다. 따라서, 위의 네 가지 한계를 극복하기 위해 후속 연구가 수행되어야 할 것으로 판단된다. 특히 첫 번째 문제점인 기후변화 시나리오의 불확실성 한계점은 후속되는 세 가지 한계점을 발생시키기에, 필수적으로 해결되어야 한다.The social and economic damage caused by climate change has increased rapidly over the last several decades, with increasing instances of heat waves, floods, and extreme rainfall. Of these, the damage caused by extreme rainfall is still ongoing, and more extreme rainfall is expected in Korean Peninsula in the future. There was up to 110.5 mm/hr of rainfall in Seoul, which caused 69 casualties and approximately USD 27.6 million in economic damage. Most of the causes of flooding in modern cities include a sharp increase in non-permeable packaging surfaces and a lack of water circulation facilities. According to climate change scenarios provided by the Korea Meteorological Administration, the average rainfall in cities over the next 100 years is expected to decrease. However, it is predicted that future instances of heavy rain will occur in the future, causing large amounts of local damage. If the current state of infrastructure is not equipped with repair or mitigating technologies, the damage will be significant. This study was conducted based on the following three objectives. First, to quantitatively analyze urban flood damage over the next 80 years (2020-2100) that could be caused by the climate change scenario provided by the Korea Meteorological Administration. Second, this study was selected disaster mitigation facilities and analyzed their impact on disaster mitigation. It also arranges and designs facilities based on an evidence-based planning. Sustainable facilities were selected by introducing eco-friendly facilities for future generations as mitigate technologies. Third, through the development of the HCFD (Hazard Capacity Factor Design) model, the capacity and performance of the facilities that may change in the future were analyzed. HCFD model was used to consider ways to maintain mitigating technologies. In order to achieve these goals, a total of three mitigating technologies have been installed. This includes water tanks, permeable pavement, and ecological waterways. In the case of water tanks, the capacity was calculated by referring to the statutes designated by the Ministry of Environment. Also, an Arc-GIS ArcHydro Plug-in was used to calculate the scale of each technology and watershed was analyzed. The precipitation provided by the climate change scenario was analyzed on an hourly basis to determine the extent to which watershed affects it, and the Huff dimensionless curve was used for this purpose. These three mitigating technologies can contribute to flooding by increasing the storage capacity of rainwater. This study suggests that all floods can be reduced by RCP8.5 in 2050, 2060. Although there will be run-off after 2070, it is analyzed that technology will significantly reduce the volume of the flood. It is deemed that a one-year analysis should be conducted in consideration of the maintenance aspects in the future. Furthermore, removal timing of the non-point source pollutant was calculated. In the case of water tanks, the amount of non-point source pollutant accumulated inside and the removal timing were calculated through MOUSE regression analysis. Internal management of water tank is classified into caution stage, general stage and safe stage. There were nine local governments that corresponded to the caution stage, ten local governments of general stage and five local governments of safe stage. There are three main conclusions drawn from the results of this study. First is that the possibility of flooding that could occur according to climate change scenarios was analyzed at a 10-year frequency. Both the RCP 8.5 scenario and RCP 4.5 scenario showed frequent flooding after 2070. For the RCP 8.5 scenario, it is predicted that the year 2090 has the highest amount of precipitation. However, for RCP 4.5 scenario 2100, the maximum daily rainfall is approximately 690 mm, with hourly precipitation of 238 mm. The second is that capacity of each technology was analyzed. According to the installation rules assumed in this study, the volume of water tanks that can be installed throughout the Seoul Metropolitan Government is 776,588 m³, permeable pavement is 89,049 m³, ecological waterway is 81,986 m³. It is siginificant that each local government has suggested an efficient combination of two technologies. Third, the amount of runoff that can be reduced by each mitigating technology was quantified. This study has identified that flooding at the local level will be more frequent and is meaningful in analyzing the quantitative effects of disaster mitigation technologies. Besides, when each local government installed flood mitigation technology in the future, quantification data would be provided to ensure optimized decision making for each situation. The limitations of this study can be diagnosed by dividing them into four parts. The first limitation is uncertainty about climate change scenarios. Since changes in carbon emissions or scenarios can significantly change precipitation values, it is believed that future studies will develop into a more significant study if a scenario with fewer errors is used. The second limitation is that the study was conducted at a frequency of 10 years, as both RCP4.5 / RCP8.5 scenarios were analyzed daily. Third, social change factors are not reflected. Fourth is the limitation of verification. In this study, an arithmetic equation and GIS Arc-hydro were used to calculate the run-off in the Seoul Metropolitan Government. The most ideal method to verification is to compare the results with other software. The reliability of this study can be improved by comparing the amount of runoff before applying technologies using programs such as SWMM, STORM, and MUSIC. Future studies, therefore, should be carried out to overcome the above four limitations. In particular, uncertainty problem of the climate change scenario should be solved.Chapter 1. Introduction 1 1.1 Background 1 1.2 Objectives 5 1.3 Scope 6 1.4 Definition of Floods 8 1.5 Vulnerability 11 Chapter 2. Literature Review 14 2.1 Overview 14 2.2 Policy Review 19 2.3 Types of Defense Technologies 21 2.4 Types of Analysis Programs 33 2.5 Target Site 37 2.6 Climate Change Scenarios 38 Chapter 3. Methodology 41 3.1 Hydrologic Analysis 41 3.2 Application of Mitigation Technology and Estimation of flood damage 46 3.3 Calculation of Current Rainfall Capacity and Run-off 48 3.4 Estimation of Hourly Precipitation in Climate Change Scenarios (RCP 8.5/RCP 4.5) using the Huff curve 51 3.5 The Concept of HCFD (Hazard Capacity Factor Design) Model for observing Future Ability Changes of Facilities 53 Chapter 4. Results 56 4.1 Site Analysis 56 4.2 The 10-year frequency flood damage analysis 65 4.3 Variation of the flooded area after application of disaster mitigating technology 71 4.4 Amount of non-point pollutant deposits in the water tank and maintenance time using the MOUSE regression equation 86 Chapter 5. Summary and Conclusions 94Maste

Establishment and Application of Spatial Distribution Model of Roof Greening Based on GIS Technology

The stage from the beginning of the 21st century to now is the stage of the scale development of roof greening(RG) in China. With the continuous progress of urban construction, on the one hand, the ecological environment is deteriorating, on the other hand, the available green space in the urban center area becomes more and more scarce. The development of this contradiction promotes the rapid development of RG. RG plays an important role in enriching urban landscape, increasing urban green quantity, reducing urban heat island effect, conserving rainwater and reducing temperature, and creating a new green space for the city, including leisure, entertainment and ecology, and improving urban ecological landscape. This paper mainly studies the establishment and application of spatial distribution(SD) model of RG Based on GIS technology. Through understanding the SD design of RG, the paper investigates and analyzes the status quo of green space of roof, macro layout and the integration of multiple functional spaces. This paper studies and establishes a multiobjective optimization model of SD of RG, and analyzes the purification effect of RG on rainwater pollutants and the overall performance of ecosystem service equity. The results show that 26.31% of the people think that the degree of RG is insufficient, and 5.14% think that RG is scarce. In the cognition of the status of RG space, 12.41% of people don't care about RG, 8.69% think it is face engineering, and even 9.31% think it is waste of resources, which indicates that the promotion of RG needs to be improved

Nature-based solutions efficiency evaluation against natural hazards: modelling methods, advantages and limitations

Nature-based solutions (NBS) for hydro-meteorological risks (HMRs) reduction and management are becoming increasingly popular, but challenges such as the lack of well-recognised standard methodologies to evaluate their performance and upscale their implementation remain. We systematically evaluate the current state-of-the art on the models and tools that are utilised for the optimum allocation, design and efficiency evaluation of NBS for five HMRs (flooding, droughts, heatwaves, landslides, and storm surges and coastal erosion). We found that methods to assess the complex issue of NBS efficiency and cost-benefits analysis are still in the development stage and they have only been implemented through the methodologies developed for other purposes such as fluid dynamics models in micro and catchment scale contexts. Of the reviewed numerical models and tools MIKE-SHE, SWMM (for floods), ParFlow-TREES, ACRU, SIMGRO (for droughts), WRF, ENVI-met (for heatwaves), FUNWAVE-TVD, BROOK90 (for landslides), TELEMAC and ADCIRC (for storm surges) are more flexible to evaluate the performance and effectiveness of specific NBS such as wetlands, ponds, trees, parks, grass, green roof/walls, tree roots, vegetations, coral reefs, mangroves, sea grasses, oyster reefs, sea salt marshes, sandy beaches and dunes. We conclude that the models and tools that are capable of assessing the multiple benefits, particularly the performance and cost-effectiveness of NBS for HMR reduction and management are not readily available. Thus, our synthesis of modelling methods can facilitate their selection that can maximise opportunities and refute the current political hesitation of NBS deployment compared with grey solutions for HMR management but also for the provision of a wide range of social and economic co-benefits. However, there is still a need for bespoke modelling tools that can holistically assess the various components of NBS from an HMR reduction and management perspective. Such tools can facilitate impact assessment modelling under different NBS scenarios to build a solid evidence base for upscaling and replicating the implementation of NBS

Urban Heat Island Effects in Tropical Climate

This paper reviews some of the characteristics of urban climates and the causes and effects of urban heat island (UHI) issues in the tropical climate. UHI effect is a kind of heat accumulation phenomenon within the urban areas due to urban construction and human activities. It is recognized as the most evident characteristic of urban climate. The increase of land surface temperature in San Juan, Puerto Rico, caused by the UHI effect was influenced by the change of land use and material types in construction. The impacts of daily temperature, surface albedo, evapotranspiration (ET), and anthropogenic heating on the near-surface climate are discussed. Analyzed data and field measurements indicate that increasing albedo and vegetation cover can be effective in reducing the surface and air temperatures near the ground. Some mitigation and prevention measures are proposed for the effects of UHI, such as a flash flood warning system

Nature-based solutions efficiency evaluation against natural hazards: Modelling methods, advantages and limitations

Nature-based solutions (NBS) for hydro-meteorological risks (HMRs) reduction and management are becoming increasingly popular, but challenges such as the lack of well-recognised standard methodologies to evaluate their performance and upscale their implementation remain. We systematically evaluate the current state-of-the art on the models and tools that are utilised for the optimum allocation, design and efficiency evaluation of NBS for five HMRs (flooding, droughts, heatwaves, landslides, and storm surges and coastal erosion). We found that methods to assess the complex issue of NBS efficiency and cost-benefits analysis are still in the development stage and they have only been implemented through the methodologies developed for other purposes such as fluid dynamics models in micro and catchment scale contexts. Of the reviewed numerical models and tools MIKE-SHE, SWMM (for floods), ParFlow-TREES, ACRU, SIMGRO (for droughts), WRF, ENVI-met (for heatwaves), FUNWAVE-TVD, BROOK90 (for landslides), TELEMAC and ADCIRC (for storm surges) are more flexible to evaluate the performance and effectiveness of specific NBS such as wetlands, ponds, trees, parks, grass, green roof/walls, tree roots, vegetations, coral reefs, mangroves, sea grasses, oyster reefs, sea salt marshes, sandy beaches and dunes. We conclude that the models and tools that are capable of assessing the multiple benefits, particularly the performance and cost-effectiveness of NBS for HMR reduction and management are not readily available. Thus, our synthesis of modelling methods can facilitate their selection that can maximise opportunities and refute the current political hesitation of NBS deployment compared with grey solutions for HMR management but also for the provision of a wide range of social and economic co-benefits. However, there is still a need for bespoke modelling tools that can holistically assess the various components of NBS from an HMR reduction and management perspective. Such tools can facilitate impact assessment modelling under different NBS scenarios to build a solid evidence base for upscaling and replicating the implementation of NBS

Flood risk management in sponge cities:The role of integrated simulation and 3D visualization

The Sponge City concept has been promoted as a major programme of work to address increasing flood risk in urban areas, in combination with wider benefits for water resources and urban renewal. However, realization of the concept requires collaborative engagement with a wide range of professionals and with affected communities. Visualization can play an important role in this process. In this research, a sponge city flood simulation and forecasting system has been built which combines hydrological data, topographic data, GIS data and hydrodynamic models in real-time and interactive display in a three-dimensional environment. Actual and design flood events in a pilot sponge city have been simulated. The validation results show that the simulated urban water accumulation process is consistent with the actual monitoring data. Use of advanced virtual reality technology can enable simulations to be placed in the wider design context including enhanced awareness of multiple functions of urban ecosystems. This procedure can therefore reduce the information communication gap and encourage innovation regarding low impact development required for sponge city construction

Wadi Flash Floods

This open access book brings together research studies, developments, and application-related flash flood topics on wadi systems in arid regions. The major merit of this comprehensive book is its focus on research and technical papers as well as case study applications in different regions worldwide that cover many topics and answer several scientific questions. The book chapters comprehensively and significantly highlight different scientific research disciplines related to wadi flash floods, including climatology, hydrological models, new monitoring techniques, remote sensing techniques, field investigations, international collaboration projects, risk assessment and mitigation, sedimentation and sediment transport, and groundwater quality and quantity assessment and management. In this book, the contributing authors (engineers, researchers, and professionals) introduce their recent scientific findings to develop suitable, applicable, and innovative tools for forecasting, mitigation, and water management as well as society development under seven main research themes as follows: Part 1. Wadi Flash Flood Challenges and Strategies Part 2. Hydrometeorology and Climate Changes Part 3. Rainfall–Runoff Modeling and Approaches Part 4. Disaster Risk Reduction and Mitigation Part 5. Reservoir Sedimentation and Sediment Yield Part 6. Groundwater Management Part 7. Application and Case Studies The book includes selected high-quality papers from five series of the International Symposium on Flash Floods in Wadi Systems (ISFF) that were held in 2015, 2016, 2017, 2018, and 2020 in Japan, Egypt, Oman, Morocco, and Japan, respectively. These collections of chapters could provide valuable guidance and scientific content not only for academics, researchers, and students but also for decision-makers in the MENA region and worldwide

A FRAMEWORK FOR SUSTAINABLE RESILIENT HOUSES ON THE COASTAL AREAS OF KHANH HOA, VIETNAM

Vietnam is a developing country and a storm-prone country in Asia. The impacts of tropical storms on Vietnam‟s residences are the main focus of study in this research. The lack of knowledge and storm-proofing techniques for improving resilient houses are unresolved issues in this place. The consequences of this limitation were demonstrated through 55% of collapsed houses and 10% of flooded areas in Nha Trang city after the storm 2017. This research was based on the community's needs to develop a set of guidance for improving stability of domestic buildings in storm-prone areas. The aim of the research is to produce a framework for designing sustainable resilient houses in Vietnam‟s coastal areas. That framework will solve a part of building problems from hurricane impacts with the resilient designs in terms of floodproofing and wind mitigation. This research also promotes the application and development of sustainable dwellings in Vietnam. Sustainable development in residences will increase building performance in two areas: energy and resource efficiency. The quantitative and qualitative data in the study were collected by the use of mixed-method approaches. Those approaches included observation, questionnaire, interview, and simulation. The observation gathered evidence of storm impacts on Nha Trang city in recent years. The community's needs were obtained with 50 responses to the questionnaire. To understand the depth of local problems, interviews with 5 local professionals and 3 householders were conducted. The main findings involved the solutions, techniques, benefits, and challenges of sustainable resilience in coastal residences. Besides, the weaknesses of existing buildings were defined through the wind simulation of Design-Builder and Autodesk CFD. The framework has three main stages for designing sustainable resilient houses in Vietnam's coastal areas. Those stages are data collection, design specifications, and product design. In particular, the framework was validated by a prototype design. The simulation results were evidence to define building performance in terms of storm resilience and sustainability. Hence, the framework and the prototype confirmed the effects of the research on society and people's awareness